Aluminum-silicon alloy and method of making it



Patented May l, 1923.

UNITED s r ras PATENT OFFICE.-

i JUNI'US D. EDWARDS. OF OAKMONT, PENNSYLV A NIA, ASSIGNO R TO AIIUMINUM COMPANYOF AMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

ALUMINUM-SILICON ALLOY AND METHOD OF MAKING I'I.

No Drawing.

T all whom it may concern p Q Be. it known that I, J UNIUS D. EDWARDS, a citizen of the United States, and a resident of Oakmont, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Aluminum- Silicon Alloys and Methods of Making Them, of which the following is a specification.

containing substantial amounts-of silicon. One object is to provide an alloy of this type having improved physical properties, especially tensile strength and ductility, and

a further object is to provide a method of producing such alloys. 4 I

he invention is based primarily upon my discovery that the addition to silicon aluminum alloys of certain metalloidsysuch as antimony or bismuth, has a marked beneficial effect upon their properties, particularly when the alloy is rapidly, cooled to complete solidification.

U'. S. Patent No. 1,410,461 to JuniusD.

Edwards, Francis C. Frary and Harry V. Churchill, discloses the fact that the tensile strength and ductility of silicon-aluminum alloys can be increased, and the grain structure' refined, by the addition of the alkali metals, sodium or potassium, to the alloys before casting them. It is characteristic of such use of these alkali metals that they are readily lost fromthe molten metal by volatilization and'oxidation, so that the molten metal must be cast promptly after their addition in order to effect the maximum improvement in the properties of the resultant alloys arising from the introduction of these alkali metals. I have found, however, that 40 if-a metalloid of relatively low volatility and relatively low affinity for oxygen, 'such asantimony or. bismuth, be incorporated in a silicon-aluminum alloy, this requirement of prompt casting no longer holds, and a marked improvement in the tensile strength and ductility larly if the alloy is caused to solidify rapidly in a chill mold according to the in vention fully disclosed in'the co-pending patent iipplication of Robert S. Archer and Junius Edwards, SerialNo. 426,839. As described in said application, the rapid solidification, of the alloy causes the; prec1pi- The invention relates to aluminum alloys of the casting results, particu-' Application filed March 18, 1922. Serial No. 544,950.

tating silicon to take the form of minute particles with a concomitant improvement in the physical properties of the alloy.

In the preferred practice of the present invention, a silicon-aluminum alloy is first. prepared in which a substantial amount of silicon is present. Silicon in small amounts, usually less than 1.0%, appears in most commercial aluminum as an impurity. The desirable properties of silicon-aluminum alldys, such for example as their low casting shrinkage, become usefully apparent only when the silicon is present in substantial amounts, say above about 3.0%, and it is alloys containing above about this percentage of silicon that are contemplated in this specification and claims as alloys containing a substantial amount of silicon. The amount of silicon present may vary from about 3.0 to 15.0%,- although'the best results are usually obtained When the silicon content is from about 8.0 to 13.0%. C The silicon-, aluminum alloy may be prepared, 'for example by stirring metallic silicon in molten aluminum at. a temperature of about 750 to 800 ,0. a

To the molten silicon-aluminum alloy, bismuth or antimony are added, preferably in a finely divided form, and thoroughly incorporated by stirring. It is advantageous to pulverize the antimony or bismuth to about 20 mesh, and to introduce them into the molten silicon-aluminum alloy by sifting over the clean surface of the alloy. The reason for this is that the density of these metall'oids is so high that they tend to sink rapidly to the bottom of the crucible, and thereafter it is difficult to thoroughly incorporate them into the specifically lighter silicon-aluminum alloy. If, however, they are reduced to small particles before introduction, thorough mixing is much more readily accomplished, particularly in the case of bismuth which'has a' limlted solubility in aluminum. The; antimony or bismuth may be added up to a content of about 1.5%" or more but the best results are secured with 0.5to 1.0% of either. These elements remain in the alloy so that the alloy may be cast at any convenient time after the incorporation of bismuth or antimony. For the reasons fully explained In said co-pending application preferably copper or zinc which, in connection with" sihcon, alloys. 110

Serial No. 426,839, the completed alloy is cast in a chill mold.

The invention is not limited to, siliconaluminum alloys containing bismuth or antimony .alone, but includes alloys having additional elements, such for example as form a series of useful aluminum It is desirable that the iron content less than 0.6%, although in some cases as much as 1.5% or more of iron might be permissible when high ductility is not essential. v While the chilled casting alone produces a marked improvement in the properties of silicon-aluminum alloys, the addition of bismuth or antimony produces an improvement in tensile strength and ductility over and above that obtained in a similarly cast alloy be kept low, preferably ple, a silicon-aluminum alloy containing 10.0% silicon, when cast with a certain deree of chill, had a tensile strength of 25,000 per square inch and an elongation of 4.0%. The same alloy cast under the same conditions after the addition of 1.0% of bismuth had a tensile strength of 30,040 lbs. per square inch and an elongation of 0.5%. A similar 10.0% chill cast silicon-alumlnum alloy showed an increase in tensile strength 0i 5,000 lbs. per square inch, and a doubling of the elongation after the addition of 1.0%

antimony.

In sand castings of silicon-aluminum alloys containin antimony or bismuth, the rate cf solidi cation is in general too slow to permit the antimony or bismuth to effect very substantial improvementsin the physical properties of the alloy. However, an increase in tensile strength of 1,400 lbs. per square in h and several percent in elongation has een obtained when silicon-aluminum alloys containing or antimony were cast in sand.

In the periodic system of the elements, antimony and bismuth, together with phosphorus and arsenic, formsub-group b of the fifth group (Roscoe and Schorlemmer, 1913, edition, volume 2, page 910), andare usually ,spoken of as metalloids, while the elements of sub-ge'oup a, with the exception of nitrogen, are more metallic in ,character and are classed with the metals. Antimony and hismuth, which are the metalloids of the fifth.

group of the periodic system of the elements having an atomic weight over 100, both act advantageously and similarly as fully-explaine'din this specification, and therefore. are classedtogether and; defined in the appended claims as metalloids of the fifthgroup of the periodic system of the elements 7 evmg an atomic weight greaterthan 100.

1 claim as my invention: I i 1. In the art of making articles of an alummum alloy containing .a substantial without bismuth or antimony. For examabout 1.0% bismuth havin substantial amount of silicon, and also conamount of silicon, the improvement comprising incorporating in a finely divided state in the molten alloy a metalloid of the fifth group of the periodic system of the elements,

having anatomic Weight greater than 100 7 and thereby favorably afi'ecting the strength} and ductility of the resulting alloy.

2. In the art of making articles of an aluminum alloy containing a substantial i amount of silicon, the improvement com- 7 an aluminum alloy containing a substantial amount of s1l1con, the improvement comprising incorporating in the molten siliconof the fifth an atomic weight greater than 100,

aluminum alloy a metalloid group'of the periodic system of the elements, having and causing rapid solidification of the molten alloy in a suitable mold.

chill castings of i 41. In the art of making an aluminum alloy contalning a substantial amount of silicon, the improvement :com-. prising incorporating antimony in the molten silicon-aluminum alloy, and causing rapid solidification of the molten alloy in a suitable mold.

5. ln the' art of making castings of an aluminum alloy containing a substantial amount of silicon, the improvement com:

prising incorporating not more than about 1.5% antimony in the molten silicon-aluminum alloy, and casting the resultant molten alloy in a chill mold.

6. In the art of making articles of an aluminum base alloy contalning from about 8.0 to 13.0% silicon, the improvement comprising ,incorporating in a finely divided state in, the molten alloy a metalloid of the fifth group of the periodic system of the elements, having an atomic weight greater than 100, thereby favorably affecting the strength and-ductility of the resulting alloy.

7. In the art of making chill cast ngs of an aluminum base alloy containing from about 8.0 to 130% silicon, the improvement comprising incorporating not more than about 1.5% antimony, and casting the resulting alloy in a chill mold:

8. An aluminum base alloy containing not less than about 3.0% silicon, and not more than about 1.5% of a metalloid of the fifth group of the periodic system of the elements,

an atomic weight eater than 100. 9. 11 aluminum base a loy containing a taining antimony.

10. An aluminum substantial amount of'silicon, and an e ec-, tive amount but not more than about 1.5% antimony. i

11. An aluminum base alloy containing .125 base alloy containin a from about 8.0 to 13.0% silicon, and an 15.0% silicon, and also containing. antimony. effective amount but not more than aboutr 14. A chill casting formcdof an alumil.5 antimony. num base alloy containing from about 3.0 12. A chill casting formed of an alumito 15.0% silicon, and an efi'ective amount but 5 num base alloy containing from about 3.0 not'more than about 1.5% antimony.

to 15.0% silicon, and a metalloid of the fifth In testimony whereof, I si my name.

group of the periodic system of the elements, J UNIUS D. DWARDS. having an atomic weight greater than 100. Witnesses: a

13. A chill casting formed of an alumi- PAUL N. CRrncHwW,

num base alloy containing from about 3.0 to I EDWIN O. JOHNS. 

